Digestion in sulphuric acid of titaniferous ore concentrates containing organic flotation agent



DIGESTION 1N SULPHURIC ACID OF TITAN- IFEROUS ORE CONCENTRATES CONTAIN-ING ORGANIC FLOTATION AGENT Thomas S. Griffin and Warren Rodgers, St.Louis, Mo., assignors to National Lead Company, New York, N. Y., acorporation of New Jersey No Drawing. Application August 17, 1953 SerialNo. 374,828

6 Claims. (Cl. 23117) This invention relates to the attack of ores. Morespecifically, it relates to the attack of titaniferous ores such asilmenite with concentrated sulfuric acid. This invention also relates tothe dissolution in strong sulfuric acid of ores containing small amountsof flotation agents.

In the preparation of ores and minerals for metallurgical treatment itis common practice to remove gangue and foreign material, andconcentrate the desired fraction of the ore by any of numerous knownprocedures. Among the procedures that have been used may be mentionedmagnetic separation, wet and dry classification,

and flotation concentration. It is with ores that have been concentratedby flotation methods that the present invention is particularlyconcerned.

The flotation agents used in the flotation concentration of ores andminerals are generally surface-active organic compounds capable ofpreferentially wetting a desired fraction of the ore, which may be, forexample, fatty acids such as stearic or oleic acid, soaps and similartypes of compounds, usually in conjunction with petroleum agents, suchas fuel oil and the like. These compounds, when used in the flotationprocess, are strongly adsorbed on or absorbed by the ore or possiblyreact with it to some extent so that it is exceedingly diflicult orimpossible to remove the last traces of organic flotation agents fromthe float fraction of the ore by normal Washing methods and the like.

When ore concentrates containing residual amounts of such flotationagents are further treated by attacking them with strong sulfuric acid,difficulties in operation are frequently encountered by reason ofchanges in the character of the reaction resulting from the presence ofthese flotation agents. Such ores foam violently and sometimesuncontrollably and the difficulties which arise from the excessivefoaming and frothing are caused by the flotation agents. In thedissolution of titaniferous ores such as ilrnenite to produce titaniumsolutions useful in the preparation of titanium pigment for example, thedigestion or attack of the ilmenite with concentrated sulfuric acid isordinarily a vigorous, rapid reaction which may, however, be controlledby using suitable digestion equipment and appropriate techniques, bothof which are well known to the art. When the ilmenite contains flotationagents the vigorous and copious foaming reaction frequently readers ituncontrollable and dangerous.

When excessive foaming takes place duriugthe digestion reaction anappreciable economic loss is sustained because the foaming carries partof the reaction mixture out of the tank altogether, while an additionalportion is removed from the heat of the reaction Zone and does not reactproperly, much of the ore remaining entrapped in the foam and unattackedby the acid.

A severely foaming ore, moreover, will actually be extruded from thetank, and the large quantities of steam and gas evolved during thereaction carry entrained ore, acid and reaction products out through thetank stack. The hot, strongly corrosive froth endangers personnel fatesPatent 2 and may cause extensive damage to equipment and structural workin the area. Moreover, the violence of the foaming is unpredictablesince the precise quantity of residual flotation agent present, and theconsequent effects thereof, will vary from batch to batch.

This element of unpredictability renders it difficult or impossible toso vary the digestion conditions as to offset the effect of theflotation agent present. The digestion reaction must be sufficientlystrong and vigorous to supply its own heat requirements, and thereforethe reaction conditions cannot be excessively mild; on the other hand,reaction condition (acid concentration, acid/ore ratio, initialtemperature of reactants, etc.) if so adjusted as to promote a normalvigorous reaction, may easily render the reaction altogetheruncontrollable when flotation agents are present.

While this invention is here described with particular reference to thedissolution of ilmenite orein concen trated sulfuric acid, it will beobviously that the invention is equally applicable to other reactivetitaniferous ores as well as to any other flotation-concentrated orewhich reacts exothermically with sulfuric acid.

Although foam-producing agents are most commonly introduced during theore-dressing operations, by flotation processes, they may also occur inthe ore for other reasons. For example, it has been suggested to sprayoutdoor ore piles with fuel oil or asphalt in order to cut down windlosses. These agents, which are similar to or identical with the fueloils used as oily collectors in flotation processes, produce the sametroublesome foaming at reaction as do the flotation agents used as such,and the process of the present invention is equally applicable to theprevention of foaming from this cause. Moreover, other but less commonsources of contamination from fuel supplies or the like will produce thesame troublesome foaming and may be effectively treated in the same way.The term flotation agents as used herein should therefore be construedto include materials such as asphalt and fuel oil, even when notactuallyused for flotation purposes.

An object of this invention, therefore, is to provide a method forrendering amenable to digestion in concentrated sulfuric :acid an oreconcentrate containing organic flotation agents. Another object is toprovide a method for treating an ore concentrate which Will overcome thetendency of residual flotation agents to render foaming at the digestionreaction violent and uncontrollable. A still further object is toprovide an economical method for treatment of an ore concentratecontaining organic flotation agents which will make possible a normaldigestion procedure with good digestion efliciencies. An additionalobject is to provide such a method which produces from a titaniferousore a re action product suitable for the manufacture of high-gradetitanium pigments and the like. These and other objects will becomeapparent from the following more complete description of the presentinvention.

In its broadest aspects this invention contemplates a method fortreating an ore containing organic flotation agents which comprisesadding to said ore a small amount of the monoglyceride of a saturatedfatty acid, said acid containing from about 12 to about 20 carbon atoms.It has been found that when such a compound is'addedto the ore inappropriate amount, which is generally between 0.01% and 0.5%,preferably between 0.05% and 0.2% on an ore-weight basis, the flotationagents present are apparently rendered ineffective or their effect isoffset so that the reaction proceeds in a normal vigorous butcontrollable manner entirely similar to the type of reaction to beexpected from a similar ore not containing residual flotation agents.

Diglycerides and triglycerides, wherein 2 or 3 respectively of thehydroxyl groups of the glycerin molecule are esterified with fattyacids, while in some cases mani testing a degree of controlling actionupon the digestion reaction, are in general not effective, especiallywhen added in economically feasible amounts. It is essential that thetreating agents of this invention contain substantially only saturatedalkyl groups since unsaturated groups, when present in substantialamounts greatly diminish or destroy entirely the ability of the treatingagents to modify and control the course of the reaction, and moreover,actually aggravate the troublesome frothing and foaming encountered inor'es which contain flotation agents.

The manner of addition of the agent to the ore appears to be unimportantproviding it is distributed in the reaction mixture prior to the actualreaction. The degree of distribution also is not critical and theordinary mixing employed during such digestion reactions appears to besufiicient to distribute the agent adequately through the reaction mass.The treating agent may, for example be added to the ore at anyconvenient stage prior to its introduction into the digestion vesselitself, or may be added to or dissolved in the sulfuric acid used forthe attack of the ore.

The quantity of monoglyceride treating agent employed should ordinarilybe from 0.1% to 0.2% of the weight of ore treated. The use of largeramounts of treating agent than those above specified is contemplated,but is ordinarily not economically justified. Smaller amounts than thosegiven above will also in some cases be efiective in controlling thefoaming at reaction depending upon the amount of residual flotationagent present. The amounts of flotation agents present in the oreconcentrate are generally extremely small. Normally, from 1 to 5 poundsof the flotation agents are employed per ton of ore in flotationmethods. The amount present in the ore concentrate is ordinarilysomewhat lower than the amount initially employed owing to partialelimination of the flotation agents during subsequent washing, drying,etc., but the major portion of the organic agents usually remainsassociated with the ore concentrate.

Owing to the difliculty of analyzing the ore concentrate for minuteamounts of residual flotation agents, and the utter impracticality ofevaluating the agents in commercial-scale digestion equipment, whichordinarily employs from 10 to 20 tons of ore and from 15 to 30 tons ofconcentrated sulfuric acid for a single digestion batch, it has beenfound more practical and desirable to evaluate the reactivecharacteristics of the ore and the quantity of monoglyceride treatmentagent required by means of an empirical test which is carried out asfollows:

A 6" I. D. cylindrical tank 14" high and having 1" steel walls and steelplate bottom is provided with an iron sweep agitator having 5 sweeps,each 5 /2 x 91 and adjusted to operate at 200 R. P. M. 1500 grams of theore to be tested are digested in this tank using the same relativeconcentration of acid, the same relative acid-to-ore ratio (based on100% H 50 and the same relative quantity of set-off water as are to beemployed in the full scale operation. Approximately half of the acid isfirst introduced into the tank, the ore is next added and washed downwith the remainder of the acid to be used. The monoglyceride treatingagent is then added, and finally the set-off water, which has the dualfunction of diluting the acid to proper strength for reaction andheating up the reaction mixture. The strongly exothermic reaction isinitiated and maintained by allowing a Meker'burner to play directly onthe bottom of the tank throughout the reaction cycle. The course of thereaction is followed by visual observation and may be recognized ascomplete when copious evolution of steam has taken place and subsided,followed by the setting-up of the reaction mixture to a rigid, porouscake ordinarily from 15 to 20 minutes after the start of heating.

When subjected to this test, an ore which does not contain flotationagents will undergo a vigorous but controlled reaction, and the reactionmass will ordinarily stay at least 4 below the top of the tank. An orewhich contains flotation agents but is treated with the mono glyceridetreating agents of this invention will behave in a substantiallyidentical manner. An ore which contains flotation agents and is not sotreated will be seen to foam violently and in many cases will overflowand project itself out of the reaction tank. The effectiveness of thequantity of monoglyceride treating agent used is gauged by the height towhich the reaction mass rises in the tank and the treatment isconsidered completely effective if the highest point reached by thereaction mass is 4 or more inches below the top of the tank. When suchis the case, the quantity of treating agent employed is suflicient forthe purpose and the same relative amount of treating agent, calculatedon an ore weight basis, may be employed safely in large-scaleoperations.

The employment of the monoglyceridc treating agents of this inventionapparently has no other observable eflect upon the course of thereaction than to offset the effect of the residual flotation agents; thereaction proceeds in substantially the same way as would be expectedwhen using a similar ore not containing flotation agents, andefficiencies and recoveries are likewise unimpaired. Addition of themonoglyceride treating agents of this invention to ores which do notcontain flotation agents has no noticeable effect.

In order to more clearly illustrate the process of this invention, thefollowing examples are presented:

Example I 1500 grams of a titaniferous iron concentrate which had beenprepared by treating a titaniferous iron ore in a flotation system with1.5 pounds of fuel oil and 1.0 pound of oleic acid per ton of theunconcentrated feed ore, was tested according to the test methoddescribed above using 1370 milliliters of 93.2% sulfuric acid and 150milliliters of water to give an acid strength at reaction of 88%. Thereaction was vigorous accompanied by extremely violent foaming; and aconsiderable portion of the reaction mass flowed over the top of thetank. The test was repeated using 0.05% of glyceryl monostearate. Thereaction in this case was accompanied by moderately violent foaming andthe reaction mass rose to within about 2 /2" from the top of the tank.The test was again repeated using 0.10% of glyceryl monostearate and thereaction was observed to be normally Vigorous but completely controlled;the reaction mass in this case never rising higher than about 5" fromthe top of the tank.

On the basis of these preliminary tests a large scale: digestion wascarried out using 10 tons of the same: titaniferous iron oreconcentrate, 16.8 tons of 93.2% sulfuric acid, 20 pounds of glycerylmonostearate and 1.1' tons of water. The reaction was rapid, completeand orderly, similar in all respects with reactions produced by ores notcontaining flotation agents. the titanium values in the treated oreconcentrate were converted to soluble titanium sulfates.

Example II Another ore concentrate was prepared by flotationconcentration of a crude titaniferous ore using 1.0 pound of oleic acidand 1.5 pounds fuel oil for each ton of raw ore treated. Approximatelyhalf of the original ore feed (together with most of the flotationagents) was collected as the flotation concentrate. After subsequentwashing and drying the flotation concentrate was tested as described inExample I using glyceryl monopalmitate as the treating agent.

On the basis of the preliminary tests another large scale digestion wasmade according to the procedure described in Example I but using 0.10%of glyceryl mono- Over of palmitate as the treating agent. The characterof the reaction obtained was substantially similar to that of Example Iand resulted in the solubilization of over 95% of the titanium values.

Example 111 An ore concentrate similar to that of Examples 1 and II wassubjected to large scale digestion according to the procedure of ExampleI, using 0.20% of glyceryl monolaurate instead of the glycerylmonostearate as the monoglyceride treating agent. Again, a vigorous,orderly reaction took place resulting in solubilization of better than95 of the titanium values.

Example IV A sample of ore taken from an ore pile which had been sprayedwith asphalt to reduce wind losses was tested in the laboratory and wasfound to have serious foaming characteristics. The amount of asphaltpresent in the ore was unknown, but laboratory tests as previouslydescribed indicated that foaming at digestion could be prevented by theaddition of 0.025% of glyceryl monomyristate. This quantity was added toa plant-scale digestion batch, With results similar to those describedin the previous examples.

As shown by the above examples, the present invention provides a methodfor treatment of ore concentrates containing organic flotation agentswhich treatment renders said concentrates amenable to dissolution instrong sulfuric acid according to the normal procedures used for suchconcentrates. The ordinary effect associated with the presence oforganic flotation agents in the ore is to render the reaction withsulfuric acid uncontrollable; by means of the present invention thisharmful and dangerous effect of organic flotation agents is preventedand the digestion proceeds as readily and conveniently as when using orewhich does not contain flotation agents. The treatment process is simpleand easy to employ.

While this invention has been described and illustrated by the examplesshown, it is not intended to be strictly limited thereto, and othermodifications and variations may be employed within the scope of thefollowing claims.

We claim:

1. A method for treatment of titaniferous ores containing organicflotation agents selected from the group consisting of anionic flotationagents, petroleum agents, and asphalt materials to render the sameamenable to attack by concentrated sulfuric acid which comprises addingto said ore a small but efiective amount of the monoglyceride of asaturated fatty acid containing from about 12 to about 20 carbon atoms.

2. In a method for dissolution in sulfuric acid of titaniferous orescontaining organic flotation agents selected from the group consistingof anionic flotation agents, petroleum agents and asphalt materials, theimprovement which comprises having present during said dissolution from0.01 to 0.5%, based on the Weight of said ore, of the monoglyceride of asaturated fatty acid containing from 12 to 20 carbon atoms.

3. Method according to claim 1 wherein said monoglyceride is glycerylmonostearate.

4. Method according to claim 1 wherein said monoglyceri'de is glycerylmonopalmitate.

5. Method according to claim 1 wherein said monoglyceride is glycerylmonomyristate.

6. Method according to claim 1 wherein said monoglyceride is glycerylmonolaurate.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Bickerman: Foams, Theory and Industrial Applications, pages301, 308, 309, Reinhold Publishing Corp., New York, N. Y., 1953.

Goldsmith: Polyhydric Esters of Fatty Acids, Chemical Reviews, vol. 33,1943, Amer. Chem. 800., page 332.

Taggart: Handbook of Mineral Dressing, 2nd ed., J. Wiley and Sons, N.Y., 1945, pages 12-120, 12-123, 12-124, 12-127, 12-38, 12-39.

1. A METHOD FOR TREATMENT OF TITANIFEROUS ORES CONTAINING ORGANICFLOTATION AGENTS SELECTED FROM THE GROUP CONSISTING OF ANIONIC FLOTATIONAGENTS, PETROLEUM AGENTS, AND ASPHALT MATERIALS TO RENDER THE SAMEAMENABLE TO ATTACK BY CONCENTRATED SULFURIC ACID WHICH COMPRISES ADDINGTO SAID ORE A SMALL BUT EFFECTIVE AMOUNT OF THE MONOGLYCERIDE OF ASATURATED FATTY ACID CONTAINING FROM ABOUT 12 TO ABOUT 20 CARBON ATOMS.